Garcia-Rodriguez et al.: Ontogenetic shifts and feeding strategies of Gadiformes in the Mediterranean Sea 59 
accounted for more than 60% of the diet of European hake. 
Species of large plankton and benthopelagic fish species 
contributed most to the diet of blue whiting (accounting 
for approximately 34% and 32% of the diet of this species, 
respectively); greater forkbeard fed mainly on shrimp spe- 
cies and species of Peracarida (Suppl. Table 4) (online only). 
Trophic ecology 
The trophic niche breadth index (B;) was highest for 
European hake, Mediterrean bigeye rockling, and silvery 
pout (Table 3). Conversely, poor cod had the lowest B; 
value, with a strong preference for red snapping shrimp 
(%V=44.1%), despite the high number of prey items (52) 
identified in its diet. 
Niche breadth across the 12 categories that are based 
on species and size class was lowest (B;=0.136) for the 
small size class of Mediterranean ling; whereas, the 
small size class of greater forkbeard ranked the highest 
(B;=0.636). 
Simplified Morisita index values ranged from 0.00 
(pair of the small size class of Mediterranean ling and 
the small size class of greater forkbeard) to 1.00 (pair 
of the large size class of greater forkbeard and poor cod) 
(Table 4). Overall, niche overlap was highest between the 
small size class of greater forkbeard and poor cod, whose 
diet had a high proportion of shrimp species, represented 
principally by red snapping shrimp. The lowest values 
were found between the small size class of Mediterranean 
ling and poor cod as well as greater forkbeard. 
The lowest and highest trophic levels were inferred for 
silvery pout (trophic level=3.51) and the large size class 
of Mediterranean ling (trophic level=4.49), respectively. 
Within this range, only Mediterranean ling and the large 
size classes of European hake and blue whiting were 
determined to be at a trophic level >4, representative of 
top predators (Table 2). For all species, with the exception 
of the greater forkbeard, which had no changes in trophic 
level with size, the large size classes were at a higher tro- 
phic level. The greatest increases in trophic level linked to 
an ontogenetic shift occurred in European hake (from 3.95 
to 4.24) and blue whiting (from 3.98 to 4.21). 
Feeding strategies 
Four groups of predators were identified on the basis of dif- 
ferent feeding strategies (Fig. 3). The first group consisted 
of species with strong preferences for decapods, such as 
the Mediterranean bigeye rockling, poor cod, and greater 
forkbeard. The red snapping shrimp was the dominant 
prey species for the large size class of greater forkbeard 
(%V=35.3%) and for poor cod (%V=44.1%), and Calocaris 
macandreae (%V=32.0%) and angular crab (%V=15.6%) 
were the main prey species for Mediterranean bigeye 
rockling and the small size class of greater forkbeard. The 
second group was composed of both size classes of Mediter- 
ranean ling, with silvery pout as the dominant prey (with 
%V values of 52.4% and 24.3% for the small and large size 
classes, respectively). 
The third group identified was composed of both size 
classes of silvery pout, which had a high preference for 
large plankton, although in the case of small silvery pout, 
species of Peracarida were also consumed. In both size 
classes, euphausiids were the most common prey item 
(with %V values of 46.8% and 36.8% for the small and 
large size classes, respectively). 
Table 4 
Simplified Morisita index values, which indicate trophic niche overlap between pairs of 12 categories of gadiform species for 
which stomach contents from specimens caught in the western Mediterranean Sea from 2011 through 2017 were examined. 
Categories combine species and size class (small [S] and large [L]; length ranges for size classes are provided in Table 2). 
Asterisks indicate extreme index values, defined as those >0.9 and <0.1. The species studied were the silvery pout (Gadiculus 
argenteus) (GAD), Mediterranean bigeye rockling (Gaidropsarus biscayensis) (GAI), Mediterrenean ling (Molva macroph- 
talma) (MOL), European hake (Merluccius merluccius) (MER), blue whiting (Micromesistius poutassou) (MIC), greater fork- 
beard (Phycis blennoides) (PHY), and poor cod (Trisopterus minutus) (TRI). 
Category GAD, GAD, GAI MOL, MOL, 
GADs 
GAD,, 
GAI 
MER, MER, MIC, MIC, PHY, PHY, TRI 
1.00 
0.24 1.00 
0.36 0.56 1.00 
0.35 0.54 1.00* 
